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Most would agree that a correct diagnosis is a key prerequisite to providing
safe and effective treatment for various illnesses. However, our diagnoses
are often a matter of opinion rather than matter of fact.

In fact, isn't it true that most diagnoses often require us to make decisions
in the absence of certainty? Our diagnoses are based on probability. This
being the case, we must use caution not to fall into the trap of making
diagnoses on the basis of faulty logic or insufficient information. It is
one thing to make a diagnosis and another to be able to substantiate it.
Though we name the things we know, we do not necessarily know them because
we name them.

Audit the diagnosis

Shortcuts in diagnostic reasoning tend to become increasingly prevalent
when veterinarians are subjected to the pressures of a high case load in
a busy hospital. In this context, short cuts are often defended on the basis
of "practicality". Although practicality is a virtue, we must
use caution not to use the concept of practicality as an excuse for ignorance.

A misdiagnosis may be more detrimental to the patient than the illness.
A wise sage once penned this thought: "Heaven defend me from a busy
doctor."

How do we know when our diagnoses are in error? If we do not have a system
designed to periodically audit our diagnoses for accuracy, we are unlikely
to recognize and correct our errors. If the accuracy of our diagnoses is
never questioned, we may become overconfident in our judgments with a tendency
to rely less and less on clinical data and more and more on our intuition.

What is the inevitable result? Experience has revealed that diagnosis
by intuition is often a rapid method of reaching the wrong conclusion.

Based on the premise that a well-defined problem is half solved, the
primary objective of this Diagnote is to review some clinical axioms that
foster the diagnostic process. An axiom is a statement universally accepted
as true.

Seven diagnostic axioms

Axiom 1: There is a difference between knowledge and wisdom.

Knowledge is facts; it consists of familiarity with information gained
by study and observation (that is, empirical experience or investigation).
Unfortunately, most of us have been taught to over-emphasize the accumulation
of new knowledge to a point where we neglect the development of acquiring
wisdom.

Whereas knowledge consists of our familiarity with relevant information
(facts), wisdom consists of the ability to properly apply knowledge. It
implies sufficient breadth of knowledge and depth of understanding to provide
sound judgment. Although essential, facts (knowledge) by themselves are
rarely of useful value. Facts are not science, just as the dictionary is
not literature.

In context of diagnosis of diseases, facts become useful only to the
extent that they can be wisely used to define, solve and prevent problems.
If we have knowledge but have not learned how to make practical application
of it, we lack wisdom.

Axiom 2: There is a difference between problem definition and
problem solution.

We use the term diagnosis in context of defining the cause(s) of clinical
signs. The ability to define a patient's medical problems without overstating
them is a crucial first step in the diagnostic process, since one must be
able to define problems before they can be solved.

No veterinarian has or ever will be trained to single-handedly solve
all types of medical problems. No one can recall enough knowledge and be
proficient with enough techniques to guarantee that (s)he alone can provide
the best care of every patient. Veterinarians can be trained to accurately
identify problems, however. They can and should be master "problem
definers."

Accurate definition of a patient's clinical problems will permit us in
our role as diagnosticians to more efficiently use available resources,
such as journals, books, the Internet, consultations and referrals, to help
resolve diagnostic problems. A problem well defined is half solved.

Axiom 3: There is a difference between observations and interpretations.

Discernment of the difference between observations (facts) and interpretations
of observations (inferences or assessments) is a critical component of the
diagnostic process. In the process of defining problems, we must use care
not to consider the meanings of observations and interpretations as equal.

Likewise, we should avoid mixing observations and interpretations randomly.
Why? Because observations and interpretations represent distinctly separate
facets of diagnosis. Consider this example. As veterinarians, we frequently
interview clients who confuse observations and interpretations when describing
the illness of their animals to us. A classic example is to misinterpret
the observation of tenesmus as constipation in a male cat with urethral
obstruction.

This type of error in reasoning is not limited to clients. It affects
us all at one time or another. For example, when asking for specific laboratory
data such as the hematocrit value (an observation), we may be told that
it is normal (an interpretation).

But a hematocrit value of 37 percent (an observation), which is interpreted
as normal may actually be abnormal in a severely dehydrated patient. Although
either observations or interpretations may be erroneous, in our experience
misinterpretation of a correct observation is the most common pattern of
error.

What is the point? A misinterpreted problem is the worst of all problems.
Why? Because if misinterpretations are unknowingly accepted as facts, misdiagnosis
followed by misprognosis and formulation of ineffective or contraindicated
therapy may result. This is indeed ironic since the patient may then be
in a worse condition as a result of having visited us in our roles as doctors.
What can we do to minimize this problem? One thing is to put the axioms
in this column into practice. An observation or an interpretation is unlikely
to mislead us if we learn how to avoid being misled.

Axiom 4: There is a difference between possibilities and probabilities.

The need to discern the difference between diagnostic possibilities and
diagnostic probabilities is another key diagnostic axiom.

In general, collection and interpretation of relevant clinical data about
a patient's illness allows us to reduce numerous diagnostic possibilities
to a few or one diagnostic probability.

However, even after collection of a large quantity of relevant data,
many diagnostic probabilities still represent a matter of educated opinion
rather than a matter of fact.

Recall that absence of clinical evidence of suspected diseases is not
always synonymous with evidence of absence of these diseases. As a corollary,
detection of evidence that is consistent with a certain, specific type of
disease is not always pathognomonic for a specific disease.

It follows that we as veterinarians should convey to our clients that
our diagnoses, prognoses and treatment recommendations are based on probability.

Axiom 5: There is a difference between disease and failure.

Discernment of the conceptual difference between organ disease and organ
failure is also fundamental to proper diagnostic refinement. Organ function
that is "adequate" to sustain homeostasis is often not synonymous
with "total" organ function.

For example, patients with only one kidney have adequate renal function
to live a "normal" life without manifestations of renal dysfunction.
Even when slowly progressive irreversible lesions occur, signs of organ
dysfunction do not develop if adequate quantities of functional parenchyma
(i.e. nephrons, hepatic lobules, etc.) remain to sustain homeostasis. This
concept is the basis for distinguishing organ disease (such as cardiac valvular
insufficiency) from organ failure (such as altered circulation associated
with abnormal cardiac rate and rhythm which ultimately occur as a result
of irreversible progressive cardiac valvular insufficiency).

Won't you agree that the approach to management of a patient with cardiac
valvular insufficiency and adequate cardiac function is very different from
management designed for a patient with cardiac valvular insufficiency and
congestive heart failure?

Axiom 6: There is a difference between clinical signs induced
by diseases and the body's compensatory response to disease-induced signs.

Clinical manifestations of disease can be subdivided into the following
two classes: 1) signs directly induced by the disease (such as impaired
urine concentrating capacity and obligatory polyuria associated with damage
to the countercurrent system in patients with bilateral bacterial pyleonephritis),
and 2) the body's compensatory response to these signs (such as compensatory
polydipsia needed to maintain fluid balance because of obligatory polyuria).

Other examples of this relationship include compensatory inflammation
in response to damaged tissue, fever in response to systemic infectious
agents, polychromasia and reticulocytosis in response to anemia, and hyperparathomonemia
in response to hypocalcemia. It follows that making a diagnosis of urinary
tract infection solely on the basis of pyuria would be an overdiagnosis
because pyuria may be a compensatory response to both infectious and noninfectious
diseases.

Axiom 7: There is a difference between events that occur consecutively
and cause and effect relationships.

The ability to recognize true cause and effect relationships is not an
innate characteristic - it must be learned. The important point to be made
here is that just because two or more events occur in consecutive order
does not prove a cause and effect relationship. Why? Because, unrelated
coincidences commonly occur in the lives of all of our patients. Consider
this example. In the late 1970's and early 1980's, vesicourachal diverticula
were cited as playing an etiologic role in some cats with lower urinary
tract disease (LUTD). Treatment by surgical extirpation was recommended
in most veterinary textbooks at that time. The observation that clinical
signs subsided coincidentally with diverticulectomy, and lack of studies
of the biologic behavior of macrosopic diverticula without surgery, reinforced
the interpretation that this anatomic abnormality was a cause of LUTD.

However, subsequent studies revealed that vesicourachal diverticula were
a sequela, rather than a cause, of LUTDs. Most of them spontaneously resolved
with appropriate medical therapy of the underlying problem. Surgery was
unnecessary. This example highlights the fact that favorable outcomes associated
with our treatments do not prove that our diagnoses were correct, or that
our treatments were.